Great advancements have been made in semiconductor technology in the last few years largely due to the discovery of new materials and the discovery of new methods of making better materials. These advances have led to new device applications for semiconducting materials and such applications often require different fabrication techniques. Typically, these techniques are aimed toward obtaining smaller size, more precise location of various geometrical features in the device, more accurate shapes for various geometrical features in the structure, greater adherence of metallic substances to the semiconductor surfaces, etc.
A particular case in point is the development of semiconductor devices involving III-V compounds containing aluminum or indium. Exemplatory compounds are GaAlAs, InGaAs, AlInAs, InGaAsP and InGaAlAs. These III-V compounds usually appear in the form of layers or thin films lattice matched or nearly lattice matched to various substrates such as GaAs and InP. Inclusion of Al or In is usually done to change optical wavelengths or permit lattice matching to the substrate. Typical devices are photodetectors, light-emitting diodes and semiconductor lasers. Generally, such devices operate at longer wavelengths than traditional III-V devices. Typical wavelengths for such devices are in the range from 0.8 .mu.m to 2.0 .mu.m, most particularly around 1.3 .mu.m.
In fabricating such devices, it would be highly advantageous to have an etching procedure which can be controlled as to etch rate, area to be etched and geometrical shape to be etched. Such an etching procedure is usually referred to as an anisotropic etching procedure. Such a procedure would be useful for making channels, via holes, mirrors, lenses, diffraction gratings and in the separation of individual chips on a semiconductor wafer.
Photoelectrochemical etching is particularly attractive as an anisotropic etching procedure. This procedure has been discussed in a number of references including U.S. Pat. No. 4,482,443 issued Nov. 13, 1984 to D. E. Bacon et al; U.S. Pat. No. 4,389,291 issued June 21, 1983 to P. A. Kohl et al; U.S. Pat. No. 4,404,072 issued Sept. 13, 1983 to P. A. Kohl et al; and U.S. Pat. No. 4,414,066 issued Nov. 8, 1983 to S. R. Forrest et al.
It is highly advantageous to develop a high speed accurate procedure for etching aluminum and indium containing III-V compounds by photoelectrochemical etching procedure.